A light emitting diode (LED) is a semiconductor element for converting electric energy into light. As compared with existing light sources such as a fluorescent lamp and an incandescent electric lamp and so on, the LED has advantages of low power consumption, a semi-permanent span of life, a rapid response speed, safety and an environment-friendliness. For this reason, many researches are devoted to substitution of the existing light sources with the LED. The LED is now increasingly used as a light source for lighting devices, for example, various lamps used interiorly and exteriorly, a liquid crystal display device, an electric sign and a street lamp and the like.
However, the LED generates much heat when turned on. If the heat is not readily radiated, the life span and illuminance of the LED are reduced and quality characteristic is remarkably deteriorated. Therefore, advantages of the LED lighting device can be obtained under the condition that the heat radiation of the LED is easily done.